In practice, cutting valves and portioning units, respectively, are known in the form of a cylinder with an axially movable piston. The mass strand is e.g. introduced via a lateral inlet into the cylinder before the partitioning piston partitions a portion by performing an axial movement and axially discharges the portion.
As a rule, either volumetric portioning units or continuously intermittently working portioning units without any volumetric portioning operation are here concerned. In the volumetric portioning process the mass is filled under a specific pressure into the defined portioning chamber, the portion is partitioned and subsequently pushed out. The size of the portioning chamber to be filled must here be matched with the size of the portion. Moreover, the maximum portion size is here limited by the maximum overall size of the portioning chamber. Furthermore, two separately controlled drives are normally needed because the partitioning or cutting function and the discharging function are performed separately. Often, only one single drive is used in the continuously intermittent portioning process. The axial drive movement of the piston with its cutting edge results in a cutting function that is not optimum because a squeezing cut with an exclusively axial pressing movement of the cutting edge of the piston is carried out in the mass strand. The product in the mass strand is squeezed more or less strongly, which leads to varying portion weights and a diffuse cutting profile in the mass strand. This is particularly disadvantageous in the case of lumpy or fibrous products of the food industry, such as sausage or ham masses, because product parts may get damaged. Large ham pieces are even drawn or squeezed into the portion. These drawbacks may even be increased by the fact that the piston bottom, which is actually used for discharging the partitioned portion, enters into the mass strand concurrently with the cutting edge, so that the pressure in the cutting area increases locally strongly and contributes to a further damaging of product constituents. The cutting edge on the rim of the piston bottom is possibly prevented from performing a clean cutting movement on the counter edge of the inlet.
It is known from DE 1 432 504 A that a stuffing piston is arranged in reciprocating fashion for portioning sausage meat in the portioning chamber, the piston first receding under the pressure of the mass filled into the portioning chamber and being then shifted by a linear drive for discharging purposes. The stuffing piston in its piston skirt has a generally U-shaped cutout with two circumferentially spaced-apart, approximately axially extending edges and serves per se only as a rotary slide and portion restrictor that in a rotary position connects the inlet to the portioning chamber and simultaneously separates the portioning chamber from the outlet, and in another rotary position shuts off the inlet and connects the portioning chamber to the outlet. There are two separate drives for linearly shifting the stuffing piston for discharging purposes and for rotating the same back and forth for switching purposes. The portioning process is a volumetric one, wherein a pressing piston is respectively adjusted in a filling cylinder connected to the inlet at a specific pressure and through a predetermined stroke. A complicated sequence control is provided for the drives. The edges of the stuffing piston perform squeezing cuts in the mass strand because the stuffing piston is only rotated for switching.
In a device known from DE 1 180 151 A, the portioning chamber contains a rotary slide which can only be rotated back and forth, and a piston which can only be reciprocated linearly, with two drives being needed for said members. The rotary slide performs a squeezing cut in the mass strand.